Field of the Invention
The present invention relates to a process and an apparatus for manufacturing tyres for vehicle wheels.
Description of the Related Art
A tyre for vehicle wheel generally comprises a carcass structure comprising at least one carcass ply comprised of reinforcing cords embedded in an elastomeric matrix. The carcass ply has end edges respectively engaged with annular anchoring structures. The latter are arranged in the areas of the tyre usually identified by the name of “beads” and each of them is normally formed by a substantially circumferential annular insert on which at least one filling insert is applied, in radially outer position thereof. Such annular inserts are commonly identified as “bead wires” and have the task of keeping the tyre firmly fixed to the anchoring seat specifically provided in the rim of the wheel, thus preventing, in operation, the radially inner end edge of the tyre coming out from such seat.
At the beads specific reinforcing structures may be provided having the function of improving the torque transmission to the tyre.
In a radially outer position with respect to the carcass ply a belt structure comprising one or more belt layers is associated, said belt layer being arranged radially one on top of the other and having textile or metal reinforcing cords with crossed orientation and/or an orientation substantially parallel to the direction of circumferential extension of the tyre.
Between the carcass structure and the belt structure a layer of elastomeric material, known as “under-belt”, can be provided, said layer having the function of making the radially outer surface of the carcass structure as uniform as possible for the subsequent application of the belt structure.
In a radially outer position with respect to the belt structure a tread band is applied, also made of elastomeric material.
Between the tread band and the belt structure a so-called “under-layer” of elastomeric material can be arranged, said under-layer having properties suitable for ensuring a steady union of the tread band itself.
On the side surfaces of the carcass structure respective sidewalls of elastomeric material are also applied, each extending from one of the side edges of the tread band up to the respective annular anchoring structure to the beads.
The traditional processes for manufacturing tyres for vehicle wheels essentially provide for the components of the tyre listed above to be first made separately from one another, to be then assembled on a proper building drum.
However, the current trend is to use manufacturing processes that allow minimising or, if possible, eliminating the manufacturing and storage of semi-finished parts.
Attention is thus now turned towards process solutions which allow making the single components of the tyre being formed by directly building them, according to a predetermined sequence, on a forming support, typically toroidal or cylindrical.
Throughout the present description and in the following claims, the term “reinforcing element” is used to indicate an element cut to size from a continuous reinforced band-like element fed close to a forming support of the tyre and comprising one or more thread-like reinforcing elements such as textile or metal cords which are substantially parallel to one another and embedded in a matrix of elastomeric material, or coated with a layer of elastomeric material.
The term: “elastomeric material”, is used to indicate a composition comprising at least one elastomeric polymer and at least one reinforcing filler. Preferably, such composition further comprises additives such as, for example, a cross-linking agent and/or a plasticizer. Thanks to the provision of the cross-linking agent, such material may be cross-linked by heating, so as to make the end product.
Throughout the present description and in following claims, the terms “radial” and “axial” and the expressions “radially inner/outer” and “axially inner/outer” are used with reference to the radial direction and to the axial direction of a forming support used for building a specific component of the tyre. The terms “circumferential” and “circumferentially” instead, are used referring to the annular extension of the forming support.
Throughout the present description and in the following claims, with “gradual laying of” a reinforcing element or with “gradually laying” a reinforcing element a non-simultaneous depositing of the entire reinforcing element on the deposition surface is meant. More specifically, a deposition carried out over an extended period of time, involving even larger portions of the element to be laid on and of the deposition surface as time passes is meant. For example, if the deposition of the reinforcing element starts at time t0=0, that is there is a first contact between the latter and the deposition surface, at time t1 comprised between about 0.05 s and about 0.1 sec. the laid area of the reinforcing element will be equal to about 50% of the area of the same and at time t2 comprised between about 0.1 sec. and about 0.2 sec. the reinforcing element will be completely laid on the deposition surface.
Throughout the present description and in the following claims, “thin plate element” or “thin plate” is used to indicate an element having a negligible thickness compared to the longitudinal and cross dimensions thereof. Preferably, the size of such thickness if of at least one order of magnitude smaller than the longitudinal and cross dimensions. Even more preferably, the size of such thickness if of at least two orders of magnitude smaller than the longitudinal and cross dimensions. For example, in the case of a longitudinal dimension comprised between about 150 mm and about 250 mm and of a cross dimension comprised between about 50 mm and about 150 mm, the thickness will be comprised between about 0.1 mm and about 1 mm.
In the present description and in the following claims, “component” of the tyre is used to indicate any part of the tyre suitable for carrying out a function or a portion thereof. Such component may for example be the liner, the under-liner, the abrasion-proof element, the bead core, the bead filler, the carcass ply, the belt strip, the belt under-layer, the tread band under-layer, the sidewall inserts, the sidewalls, the tread band, the reinforcing inserts.
WO 2010/067139 describes a process for manufacturing tyres for vehicle wheels, wherein an annular reinforcing structure is associated at each of the axially opposite end edges of a carcass ply laid on a substantially cylindrical forming support, such annular reinforcing structure being obtained by deposition on the carcass ply of a plurality of reinforcing elements cut to size from a continuous reinforced band-like element fed close to the forming support. The deposition of the reinforcing element comprises the positioning of the reinforcing element on the end edge of the carcass ply by moving a special positioning member and after that, the complete laying of the reinforcing element on the end edge by exerting a pressure with a proper pressing member separate from the positioning member. Such pressing member is provided with a plurality of spring elements.